The invention is generally directed toward a crane warning system and more particularly directed toward a crane warning system utilizing a pneumatic function generator.
Users of crane and other boom-type load lifting devices continually fight hazardous working conditions with respect to overloading. The criteria used in determining overloading include a computed load capacity based upon the type of crane, the length of the boom, and the boom angle. At any given boom angle and boom length there is a computed load capacity for the crane. This is the maximum loading in order to have safe working conditions. In many instances the operator is called upon to determine safe conditions based on his experience and boom angle and length.
Several efforts have been made in the art to automatically indicate a safe or hazardous condition regarding weight on boom-type lifting devices. One such system is manufactured by Dillon Corporation under the name Cranegard, the Cranegard system is an electronic system using load indicators to measure and display the crane's hookload as a percentage of a preset load limit. The limit is selected by the operator and is determined by the type of crane, boom length, indicated boom angle, and other operating conditions. Internal system relays will activate an audible alarm when that limit is exceeded.
A second crane monitoring system is marketed by Tood Research & Technical Division located in Galveston, Tex. under the name TRT Crane Monitor System. This system is also electronic in nature with the signal from a load cell conditioned electronically and displayed on an appropriate load meter.
The Sheave Master System 20 manufactured by Sheave Master Inc., Addison, Tex.; and, the SEQ crane overload warning system manufactured by SEQ Systems, Laporte, Texas, are further examples of load indicating systems for crane and other load lifting devices. The Sheave system utilizes a boom angle sensor and load sensors for delivering electronic signals to a logic module for purposes of calculating hazardous loading conditions. The SEQ crane overload warning system is a solid state electronic device operating on a load moment theory. This system also includes a display module, electronic module, a boom angle sensor, load sensor and interconnect cables.
In all of these systems the operator will set the maximum load limit based on his experience, and knowledge of the boom angle. This limit will be set based upon a loading chart showing boom angle as a function load along with knowledge of the operator regarding his crane system. None of these devices indicates the use of any instrumentation that will automatically calculate the maximum load setting based upon a boom angle sensor signal. Further, a major disadvantage of these systems is in their electronic characteristic. For oil well uses, especially on offshore rigs, any warning system must be explosion proof. Use of electronic systems and the need to make them explosion proof significantly increases cost.
It is further recognized that the functional relationship between the boom angle and the load is a non-linear relationship. In view of the need for an explosion proof system and thus a desireability to have the entire crane warning system to be pneumatic and yet fully automatic, the use of a function generator to translate the linear boom angle signal to the non-linear load signal is advantageous. There are no known pneumatic function generators in the art capable of translating a linear to non-linear signal.